This is a study of the effect of three common neonatal stress mechanisms, hypoxia, hypothermia and glucose feedings, on regional perfusion using nucleotide-labeled microspheres. The model is the 1-5 day old anesthetized piglet with a left atrial transeptal catheter and two distal aortic catheters. The 15 plus or minus micron microspheres are injected in the atrium before and, with a second different label, after a 30-minute stress period utilizing the above stress mechanisms singly and in combination. Our study of the individually applied stresses has demonstrated that hypoxia produces no significant change in cardiac output (CO) but a significant decrease in blood flow to the mucosa of the small intestine with a simultaneous increase in total hepatic blood flow. Mild hypothermia (3-4 degrees (C) decreases CO and also blood flow to the small and large intestine with the greatest decrease to the mucosa. Total hepatic blood is not significantly decreased. Gastric glucose instillation produces a significant increase in CO and blood flow to the colon without other significant changes. We plan further studies of regional perfusion utilizing these stress mechanisms in combination. We are also developing a new model to allow determination of the amount of central vascular shunting which occurs and may be contributing to the above noted effects.